For the fans, it is a biannual treat and an entertaining day of wicked whispers, speculation and gossip.

For the clubs, it is the last chance saloon - the final opportunity to snap up a bargain and strengthen their squad.

But for the doctors and physios, transfer deadline day is a whirlwind. With anxious clubs breathing down their necks and the clock ticking, it's down to them to deliver the cold, hard facts about a player's injury risk to the buying manager and money men backing him.

Sportsmail went to St George's Park in Staffordshire recently to gain an insight into what exactly goes on in a football medical.

VIDEO Scroll down to watch James Rodriguez and Thomas Vermaelen undergo medicals

Make or break: James Rodriguez is seen undergoing an ECG during his medical before joining Real Madrid this summer. The medical is an integral part of the transfer process and a bad report can scupper a deal

AGAINST THE CLOCK

On Monday, dozens of players will be moving clubs and swapping the familiar for the unknown. Many deadline day moves come about without much prior warning but it is still essential the buying club know as much as possible about their new acquisition.

After all, you wouldn't want to be sold damaged goods in the supermarket and football is no different, especially with large transfer fees changing hands.

A standard medical can take up to 48 hours, factoring in the travel times transporting the player to and from hospital for their scans. On deadline day, this time is simply not available.

So for medical teams like the one at St George's Park, the aim is to gather as much information as quickly as possible and then go back to the manager and the club's board with a frank, accurate assessment on the player's injury risk. The club will then decide whether to go through with the deal.

Steve Kemp, an elite physiotherapist based at St George's who works with the England team, says: 'For a physio, deadline day is an absolute nightmare. The clock is counting down and you can't do that full medical.

'It won't be as informed a decision as it could be because we don't have all the scans we would like. When the deadline comes, you simply aren't going to get the same amount of information and it's then up to the board and the manager to decide whether to take that risk.'

Check-up: Dr Zaf Iqbal gave Rickie Lambert the once over before the striker signed for Liverpool

RESEARCH AND PREPARATION

Planning is half the battle in any medical. The more knowledge that can be accumulated prior to the medical, the more focused the check-up can be - particularly important when time is tight.

If a player has a known track record of ankle problems then a scan on the ankle will be arranged as the priority.

Ethically, clubs should share the full dossier on a player's fitness and injury record with the buying club but this doesn't always happen.

So it requires a combination of the club's analysts and medical staff to build-up a detailed back history of those niggles and injury absences.

Knee-sy does it: Luis Suarez has his joints checked out by the doctor before joining Liverpool

Dr Charlotte Cowie, Clinical Director at St George's Park, says a full medical would include a complete checklist of every joint and muscle in the body, with notes of any previous problems.

A deadline day medical, because of the circumstances, cannot be that comprehensive and must be tailored.

Steve Kemp says: 'I'd like to think the clubs know everything. The players have their medical notes and, ethically, they should be passed on.'

He adds that in 10 years time, the introduction of the Premier League's long-term Elite Player Performance Plan (EPPP) will mean all medical histories will be stored on a central database and shared between clubs.

Listen up: Brazil's David Luiz has his hearing tested prior to the World Cup

TEST OF STRENGTH

Armed with a player's medical history, the team can now begin the carefully-chosen series of tests that will make or break the transfer.

The physios will first want to undertake a muscular and skeletal assessment and this usually means a trip to the nearest hospital for a Magnetic Resonance Imaging (MRI) scan.

These are the large tube-shaped machines around a moving bed. Because the focus is usually on the lower half of the body - notably the feet, ankles and knees - the player will go in feet first. It can take up to half an hour to go through.

As the player continues the medical, the experts will pore over the data and try to identify and weak points in the bones, muscles and joints.

Another key test involves using a dynamometer. This elaborate piece of kit is the most accurate way to measure leg strength.

Heartbeat: Gareth Bale has his circulatory system tested before his world record £87m move to Real Madrid

The player will be strapped into a harness on the seat and have their leg weighed. From the sitting position, they extend their lower leg upwards with varying degrees of force.

For the warm-up, the player is required to lift their leg twice at half-force, twice at three-quarter force and twice at full speed. It's then six reps at the slower speed and six at the maximum.

The computer then calculates the ratio of strength between the quadriceps and the hamstrings in the upper leg and also measures which of the legs is the stronger.

Again, the aim is to assess how strong the player's legs are and identify any areas that are possibly susceptible to injury.

TICKING OVER

The heart and circulatory system is the next focus. Blood tests will have been taken in the hospital to ensure there are no liver or kidney problems with the player.

They will also have an Electrocardiogram (ECG) - that's the test with the little electrodes stuck to your arms and chest connected to wires.

Please turn over: Thomas Vermaelen on the hospital bed prior to his move to Barcelona from Arsenal

These sensors detect the various impulses coming from the heart and will pick up an abnormal heartbeat or any other circulatory problems.

As fit, young individuals, footballers should be fine with this test but a detected heart problem is a career-ending issue.

BREATHE IT IN

Players will cover up to 10 miles during the course of a match, so it's critical they have a high aerobic capacity - getting air in and out of their lungs.

That's where the VO2 max test comes in. It takes place on a treadmill like you'd find in any gym, but one with a few modifications.

You wear an oxygen mask connected to a pump and a nose clip while running, making you feel as though you're underwater.

Jog on: Sportsmail's Adam Shergold takes part in a VO2 max test on the treadmill at St George's Park

Breath it in: Shergold bites down on an oxygen pump while wearing a nose clip during the test

My run is for a mere four minutes at a brisk jogging pace. The footballers must do a test until 'exhaustion' in their medicals - i.e. faster and faster until they can take no more.

Sports Science Lead at St George's, Carl Wells says they begin at a speed of 8km/h and this is ramped up by 1km/h each minute. The usual maximum is around 20km/h.

My results show I'm reaching a comfortable plateau in oxygen intake about about two minutes, as is the norm for non-athletes.

The players' graph will incline more sharply before eventually levelling off.

WHAT HAPPENS NEXT?

Once all the data is collated, it's time for the experts to take a good look over it and reach their conclusions for the benefit of the club, who will make the final decision.

Kemp says: 'In my career, I've never 'failed' someone in a medical but I've passed the information on to the manager and said: 'he's at a moderate risk or a high risk of injury, he's missed 40 per cent of the last two seasons, he 's down on this, he's had this etc. I would suggest in the next two years he will have x,y and z injury that you'll have to manage.'

'And if the manager really wants that player and is willing to take that risk, then he is signed.'

But how do the players take it?

'Normally, they're frustrated that you're bothering them for 48 hours and following them around! You're in taxis going to different scans. The scans themselves can take up to six hours. That is draining for six hours and the whole process can take 1-2 days. Generally they're brilliant, one or two get a bit frustrated because that's the modern footballer for you.'

Results are in: Shergold and Sports Science Lead Carl Wells analyse the graph after the VO2 test

Perform St. George’s Park is the official healthcare provider for The FA National Training Centre in Burton-on-Trent. The cutting-edge sports medicine and human performance facility is open to elite athletes and the general public alike.